DESCRIPTION: This proposal is based on the hypothesis that axonal loss is the major cause of irreversible neurological signs and symptoms in multiple sclerosis patients. The principal investigator has designed a series of experiments to address fundamental questions regarding axonal loss and other axonal lesions in multiple sclerosis plaques and in two animal counterparts (Aims 1-3); he also intends in Aim 4 to assess the status of oligodendrocytic precursor cells in and around multiple sclerosis plaques. Multiple sclerosis spinal cord, almost exclusively postmortem, will be obtained by rapid autopsy; axonal counts from these patients versus controls will be collected by morphometric techniques and subjected to statistical analyses. Similar manipulations will be performed on animal models of inflammatory demyelination and experimental spinal cord trauma. The investigator proposes in Aim 1 to quantify axons, terminal ovoids, and myelin sheaths in MS spinal cord sections immunostained with antibodies to neurofilaments, both phosphorylated and non-phosphorylated, proteolipid protein and MHC class II molecules through a morphometric analysis of the demyelinative plaques, as well as periplaque proximal and distal axonal reactions. These measurements will be made in acute to chronic plaques and compared to each other and to controls. Confocal microscopy of double-labeled fluorescent preparations will be a major source of this data. The axonal lesions will be correlated with tissue levels of N-acetyl-aspartic acid, utilizing HPLC, in sections serial to the ones studied morphologically. This same approach will be used in rat spinal cord (Aim 2), which has been transected and examined at 2, 7, 14, 16, and 120 days post-transection. Aim 3 is to do a comparable analysis utilizing a mouse model of chronic relapsing EAE that has been induced through the administration of a portion of the proteolipid protein. The final series of experiments (Aim 4) will attempt to characterize the distribution and determine the functional subpopulations of oligodendrocytic precursor cells in acute and chronic multiple sclerosis lesions by using antibodies to NG2, PDGFar, GRO-ar, erbB 2,3,4, P75 plus Trk A, p75 minus Trk A, fas, and activated caspase 3.